1. Field of the Invention
The invention relates to an optical sensing system for use in a freezing environment and more particularly to a system for protecting optic elements, which form part of an optical sensing system used in a freezing environmentxe2x80x94such as in a freezer compartment of a refrigerator, from moisture or ice build-up.
2. Description of Related Art
Many applications require the monitoring of the contents or level of a container. One such application is in automatic ice making systems for use in a home refrigerator. Typically, ice making systems include an ice maker mounted within the freezer compartment of the refrigerator and an ice storage receptacle or bin supported beneath the ice maker for receiving the formed ice from the ice maker. U.S. Pat. No. 4,942,979, to Linstromberg et al. is an example of a prior art ice making system.
In the design of ice maker systems for refrigerators, it is recognized that a control system must be provided for sensing the level of ice disposed in the ice storage bin such that ice pieces are produced when insufficient ice is in the storage bin and ice pieces are not produced when the ice storage bin is filled. A typical ice level sensing system, illustrated by U.S. Pat. No. 5,160,094, to Willis et al., includes an ice maker which employs a bail arm which is periodically lowered into the ice storage bin and then raised back out of the ice storage bin. If the presence of ice pieces interferes with the bail arm being lowered into the ice storage bin, the ice maker is deenergized such that more ice pieces are not produced.
Conventional ice level sensing systems such as the one disclosed by Willis et al. have several drawbacks. Firstly, these mechanical linkage type systems include many moving parts which are subject to failurexe2x80x94particularly in the relatively harsh environment of a freezer. Moving parts may readily become frozen under some circumstances causing the level sensing system to fail. Secondly, conventional ice level sensing systems are not easily applied to a refrigerator ice making system having a door mounted ice storage bin. Door mounted ice storage bins offer several advantagesxe2x80x94including making more space available for freezer shelving. However, if a conventional bail arm type ice level sensing system is used with a door mounted ice storage bin, damage may readily occur to the bail arm if the refrigerator door is opened when the bail arm is being lowered into the ice storage bin.
U.S. Pat. No. 3,635,043, to Sterling, is directed to a refrigeration system including a door mounted ice storage receptacle. Sterling discloses having a photoelectric system employing an incandescent lamp 54 and a photocell 55xe2x80x94for sensing the level of ice in the door mounted bin. The lamp 54 is continuously on and shines a light beam across an ice storage bin. When the beam of light is interrupted by accumulated ice, ice harvesting is prevented. Unfortunately, the system disclosed by Sterling consumes a relatively large amount of energy. Moreover, the incandescent lamp, being continuously on, will have a relatively short lifexe2x80x94requiring frequent bulb replacement.
U.S. Pat. Nos. 4,984,462 and 4,920,336 also disclose photoelectric or optic systems for measuring the contents of a container. U.S. Pat. No. 4,920,336 is directed to a system for monitoring the level of fluid in reservoirs to progressively administer solutions to hospital patients. U.S. Pat. No. 4,984,462 discloses monitoring the liquid level in batteries.
The present invention is directed to a unique manner in which optical elements can be protected from moisture and/or ice build up when used in freezing environment, such as a freezer compartment of a refrigerator.
More particularly, the present invention is directed to a hood or sleeve which can be assembled to an optical element such as a light emitting or receiving element used in a freezer compartment and which acts to trap air about the optic element such that warm humid air does not readily move into contact with the optic element. Moreover, the warm, humid air that does flow toward the optic element may be cooled by the sleeve such that moisture condenses out of the air and onto the sleeve. In this way, the sleeve acts as a type of getter or desiccant, removing moisture from the air surrounding optic element.
Still more particularly, the present invention is directed to an optical system for sensing the level of contents within a container which is disposed within a freezing environment. The system includes an emitter assembly which comprises a printed circuit board, a light emitting element mounted on the printed circuit board and a heater resistor mounted on the printed circuit board and disposed adjacent the light emitting element. A first sleeve is disposed about the light emitting element and is secured to the first heater resistor. The system also includes a receiver assembly which comprises a second printed circuit board, a light receiving element mounted on the printed circuit board and a second heater resistor mounted on the second printed circuit board disposed adjacent the light receiving clement. A second sleeve is disposed about the light receiving element and is secured to the second heater resistor. The sleeves act to trap air about the optic elements such that warm humid air does not readily move into contact with the optic elements. Moreover, the warm, humid air that does flow toward the optic elements is cooled by the sleeve such that moisture condenses out of the air and onto the sleeve.